磁铁矿反射色与硅含量的耦合变化

A coupling variation between reflected color and Si content of magnetite

Si能以类质同象形式赋存于磁铁矿的晶体结构中,从而导致晶体结构畸变。那么,这种晶格畸变是否可以改变其反射色呢?为了探究反射色与硅含量之间是否存在耦合变化关系,本文选取青海白石崖矿床中的条带状铁矿石为研究对象,利用光学显微镜观察到磁铁矿的反射强度出现了明显变化,表现出从浅灰色到深灰色的突变特征。研究表明,这种差异性的变化与磁铁矿中SiO_(2)含量有非常密切的关系:当SiO_(2)的含量较高时,磁铁矿的反射率明显下降,反射色偏暗;反之,当SiO_(2)含量较低时,磁铁矿的反射率也要高一些,反射色偏亮;即背散射图像与反射色图像表现出一一对应的关系,存在着耦合变化的情况。一般认为,硅进入磁铁矿晶格中时,会导致空位的产生。当SiO_(2)的含量增多导致空位占比明显增加的时候,一部分入射的光线进入到空位中的时候无法反射,从而降低整体的反射率。

Silicon can substitute iron in form of isomorphism in magnetite crystal structure, resulting in the lattice distortion of magnetite. Whether or not this lattice distortion can change the reflected color of magnetite remains unknown.In this work, the banded iron ores from the Baishiya deposit(Qinghai Province) were investigated to explore if there is a potentially coupled relationship between reflected color and silicon content of magnetite. The studied magnetites have different reflection colors varying from light grey to dark grey under optical microscope. This research shows that the variation of reflected color intensity is closely correlated to silica content of magnetite. When the magnetite has relatively high silica content, its reflectance decreases and reflected color is relatively dark. In contrast, when the magnetite has relatively low silica content, its reflectance is relatively high and reflection color is relatively bright. This means that there is a one-to-one correspondence between the back scattered image and the reflected color image. Generally, it is believed that the replacement of iron by silicon in magnetite crystal structure leads to the formation of vacancy in the lattice of magnetite. When the proportion of vacancy is increased due to the increased silica content in magnetite, a portion of the incident light entering the vacancy cannot be reflected, resulting in a decreased overall reflectivity for the magnetite.